1. Technical Field
The invention generally relates to methods and compositions for diagnosing breast cancer, and, more particularly, to such methods and compositions which use the differential expression of protein biomarkers in the saliva of an individual to differentiate among ductal carcinoma in situ of the breast, benign fibroadenoma and non-cancerous tissue in that individual.
2. Description of Related Art
Conventional physical examination and mammography are useful screening procedures for the early detection of breast cancer. However, they can produce a substantial percentage of false positive and false negative results especially in women with dense parenchymal breast tissue. Consequently, screening results in a number of negative biopsy results yielding a high percentage of false positives. There is also a demonstrated lack of sensitivity in detecting cancerous lesions in younger women yielding a significant percentage of false negatives. Although advanced technology in the field of mammography allows more reliable detection of small lesions of the breast, a clear need exists for added modalities of screening, particularly for diagnosing cancer in younger women.
There has been extensive use of immunohistochemistry to detect expression of specific biomarkers as a potential adjunct diagnostic procedure for certain tumors. Primarily, the markers have been found in serum and in tissues. Protein tumor markers such as c-erbB-2 (erb) and Cathespin-D (CD) have been assayed in tissue and shown to correlate with aggressive lesions.
The term “proteomics” was originally defined to represent the analysis of the entire protein component of a cell or tissue, but that term now encompasses the study of expressed proteins, including identification and elucidation of the structure-function relationship under healthy conditions and disease conditions. In combination with genomics, proteomics can provide a holistic understanding of the biology underlying disease processes. Information at the level of the proteome is critical for understanding the function of specific cell types and their role in health and disease (1, 2).
Protein expression and function are subject to modulation through transcription as well as through posttranscriptional and translational events. Multiple RNA species can result from one gene through a process of differential splicing. Additionally, there are more than 200 post-translation modifications that proteins could undergo that affect function, protein-protein and nuclide-protein interaction, stability, targeting half-life, and so on (6), all contributing to a potentially large number of protein products from one gene. Identifying and understanding these changes are the underlying themes in proteomics (6-9).
Technological advancements have benefited proteomic research to the point where saliva is now being assayed for protein content using the latest available proteomic technology (10). There is a paucity of information regarding the salivary proteome and its constituents in the presence of disease such as carcinoma. One inventor's previous studies using immunological techniques have demonstrated that saliva from breast cancer patients exhibited elevated levels of c-erbB-2, CA 15-3, EGFR, cathepsin D and p53, suggesting that there is communication between the breast tumor and the salivary gland (11, 12). In single analyte reports, additional low-abundance proteins such as HER2/neu, Waf-1, pantropic p53, EGFR and cathepsin D were found to be altered (12). Recently, the tumor biomarkers CA 125, c-erB-2 (erb) and Cathespin-D (CD) have been detected in saliva and employed in a diagnostic panel for the initial detection and follow-up screening of breast cancer patients. There is continuing interest in the development of adjunct diagnostic procedures to enhance breast cancer screening.